Printed circuit boards comprise a plurality of circuits, the density of which on the circuit boards is increasing all the time as miniaturization of electronics components continues.
Known circuit board test apparatus or fixtures, respectively, can be basically divided into two classes. Belonging to the first class are the so-called parallel testers, i.e., test apparatus having an adapter in which all circuit board test points are contacted simultaneously by means of the adapter. The second class comprises the so-called finger testers, these being apparatus which sequentially scan the individual circuit board test points by two or more finger probes.
Adapter-type test apparatus are disclosed, for example, in DE 42 37 591 A1, in DE 44 06 538 A1, in DE 43 23 276 A, in EP 215 146 B1, and in DE 38 38 413 A1.
Such adapters basically serve to adapt the irregular configuration of the circuit board test points of the board under test to a given grid pattern of the electrical test apparatus. In the case of modem boards under test, these test points are no longer arranged in a regular grid pattern, this being the reason why the contact nails producing the connection between the contact grid pattern and the circuit board test points are arranged tilted or deflecting in the adapter or a so-called translator is provided which xe2x80x9ctranslatesxe2x80x9d the regular contact grid pattern into the irregular configuration of the circuit board test points.
Depending on the type of apparatus involved, the individual circuits are tested for open circuits in the circuits (xe2x80x9copen-circuit testxe2x80x9d) and for shorts to other circuits (xe2x80x9cshort-circuit testxe2x80x9d). The short-circuit test may involve detecting both low-impedance and high-impedance shorts.
Various test methods are known for both open-circuit and short-circuit testing, in which each circuit is tested for a short circuit or each branch of a circuit tested for an open circuit. Generally, modem circuit boards having a plurality of circuits require a corresponding large number of individual test procedures to be carried out.
Attempts have been made to optimize the individual test procedures and to minimize the number thereof. A plurality of differing methods have been proposed and put into practice for this purpose.
Known furthermore are apparatus for testing componented circuit boards (e.g., WO96/27136). Testing componented circuit boards is principally different than testing non-componented circuit boards since in the case of componented circuit boards a so-called function test may be implemented. As a rule, each circuit of the circuit board is contacted at one point only and a voltage or current value is sensed which varies as a function of predetermined voltages or currents. This is possible since in the case of componented circuit boards all function elements (ICs, transistors, resistors, capacitors, etc.) are present and their function can be tested. The number of contacts made between the test apparatus and the board under test is thus significantly less when testing componented circuit boards than when testing non-componented circuit boards.
Conventional apparatus for testing componented circuit boards and implementing the function test comprise an adapter, the probes of which require complicated wiring. As compared to such test apparatus, WO 96/27136 provides for an adapter system having a grid base on which several contact pads are electrically connected to each other via test channels. These contact pads are positioned on the grid base in a mixed distribution. The grid center-spacing of the grid base is usually 1.27 mm. The wiring is thus integrated in the grid base. Such an apparatus is unsuitable for testing non-componented circuit boards which need to be contacted with a much higher contact density.
The invention is based on the object of providing a test apparatus for testing non-componented circuit boards with which circuit boards having a high circuit board test point density and/or a very small circuit board test point center-spacing can be tested.
This object is achieved by a test apparatus, for testing non-componented printed circuit boards, comprising an electronic analyzer electrically connected to a grid pattern, whereon an adapter and/or translator is mounted. The circuit board to be tested is then placed on the adaptor and/or translator. The adapter and/or translator produces an electrical contact from the circuit board test points on the circuit board to contact points of the grid pattern. At least two contact points of the grid pattern are electrically connected to each other. The contact points comprise at least in some portions a center-spacing (a) of 800 xcexcm or less.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.